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聚合物蓄冷剂是一种新型蓄冷材料,目前对于其性质尤其是微观机理研究较少。本文在等温-等压系综下采用分子动力学模拟方法研究了不同小分子醇类(乙二醇、甘油、丙二醇)对聚乙烯吡咯烷酮(PVP)、聚乙二醇(PEG)两种聚合物水溶液蓄冷剂在不同温度下的动力学特性,并从氢键分布与体系平衡态、径向分布函数、扩散系数等角度进行了分析。结果表明:温度对于蓄冷剂影响较大,温度越低,分子动能越小,分子运动越平缓,氢键结合力越大,体系黏度增大,扩散系数减小,有序性增强,进而完成由液相到固相的转变;在PEG-甘油–水体系中模拟相变温度为253.15 K附近,与实验值255.6 K吻合良好,当温度从293.15 K降至243.15 K时,PEG-乙二醇/甘油/丙二醇–水三种体系扩散系数分别降低了67.7%、69.1%、73.8%。研究结果对于筛选和制备高性能的复合蓄冷材料具有一定的参考价值和指导意义。 相似文献
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回热器是脉管制冷机的关键部件之一,其效率对脉管制冷机性能有很大影响。铅丸是常见的蓄冷材料,通常用于回热器的低温端。本文测试和分析了不同品质的国产铅丸和进口铅丸对单级G-M型脉管制冷机性能的影响。采用额定功率为6.0 kW的压缩机驱动,使用进口铅丸脉管制冷机最低制冷温度达12.9 K,这是当前单级脉管制冷机达到的最低制冷温度;40 K时的最大制冷量为57.4 W。使用国产铅丸最低制冷温度为13.6 K,40 K时的最大制冷量为55.9 W。本文对低温制冷机蓄冷材料选择具有一定的参考价值。 相似文献
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文章详细描述了针对低温真空泵用的紧凑型两级G-M制冷机的实验系统和测试方法;试验测试了不同的蓄冷材料,尤其是磁性蓄冷材料来提高制冷机性能;在一种结构十分紧凑的两级G-M制冷机上,在12K获得了4W的制冷量,最低制冷温度为7.3K。文中还对该制冷机在没有吸附装置的情况下做了对比实验研究,有利于扩展G-M制冷机的用途。 相似文献
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Due to the deformation of electronic charge clouds, the Dick-Overhauser exchange charge in ionic materials is shown to have quadratic temperature dependence as T tends to zero in non-centrosymmetric crystals. It follows that the pyroelectric coefficient π has a linear temperature dependence in the same low temperature limit. The order of magnitude of π obtained theoretically by a simple model at T = 5 K is 2 × 10?7 μC cm?2 K?1, which is in fairly good agreement with that obtained experimentally on LiTaO3 by Lines. 相似文献
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Arthur Komar 《General Relativity and Gravitation》1995,27(11):1185-1206
A measurement theory for the temperature of relativistic systems is developed. The resulting operational approach is shown to be quasi-local and therefore may be applicable in general Riemannian manifolds even when there are temperature gradients which induce heat flows. The surprising feature of our analysis is that it leads to a bifurcation of the temperature concept into two distinctly different measurable quantities: one a frame invariant scalar field which a local co-moving observer would tend to identify with the local temperature and employ in the definition of entropy, the other a frame dependent, but nevertheless locally determinable quantity which governs the flow of heat and the ability to extract work. The two quantities differ by the bookkeeping methodology employed to calibrate the thermometer. A simple relationship between the two temperatures can be established if a preferred Killing vector field is available in the Riemannian manifold. 相似文献
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A. H. Cai X. Xiong Y. Liu H. Chen W. K. An X. S. Li Y. Zhou Y. Luo 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(2):147-151
We propose expressions for the estimation of the isenthalpic temperature T
0 (T
0 = αT
m
, α is a semi-empirical parameter and 0 ⩽ α < 1, T
m
is the solidus temperature) and the Kauzmann temperature T
k
(T
k
= T
m
exp(α−1)) for glass forming alloys. It is found that T
k
estimated by T
k
= T
m
exp(α−1) is in agreement with that directly calculated from the heat capacity data, indicating that T
k
= T
m
exp(α − 1) can be used to estimate T
k
of glass forming alloys. T
0 estimated by T
0 = αT
m
, on the other hand, widely deviates from that of directly calculated from the heat capacity data. This suggests that the
enthalpy difference of the under-cooled liquid and the crystal might be a nonlinear function of the temperature below T
k
. Moreover, the Gibbs free energy difference ΔG is not sensitive to the deviation of α. 相似文献
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Non-equilibrium carrier distributions were obtained in CdS at various temperatures from 77 to 400K. A study is made of the influence of the lattice temperature on the carrier temperature. It is found that the higher the lattice temperature the lower is the difference between carrier and lattice temperatures, though carriers are always thermalized among themselves. The results can be accounted for by carrier relaxation through optical polar phonon emission. 相似文献
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《Physica A》2005,358(1):49-57
The expressions for the nonequilibrium temperature derived from the fluctuation–dissipation theorem and from the differential of the informational nonequilibrium entropy for ideal gases under shear flow are compared. Both temperatures are different, in particular, the thermodynamic temperature derived from the entropy is lower than the local-equilibrium temperature, whereas the effective temperature defined from the fluctuation–dissipation expression is higher than the local-equilibrium temperature. 相似文献
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Ying Lu Zuying Zhang Wei Guo 《International Journal of Infrared and Millimeter Waves》1996,17(9):1567-1571
Based on the transmission-line theory, this paper describes a new procedure to calculate the radiation from layered media with nonuniform temperature profile. The result is compared with those obtained through the incoherent method and the analysis of the electromagnetic fields. 相似文献
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The transit times of ultrasonic waves have been measured in single crystal NbO2 from 295 K down to 1.5 K for quasilongitudinal and shear waves propagating in the [100] direction and down to 160 K for eight other waves. Values are obtained for the C44 elastic constant and for an elastic constant combination which is approximately equal to C11 for temperatures down to 1.5 K and for C11, C12, C13, C16, C33, and C66 down to 160 K. These results are used to deduce 0 K values for the elastic constants and an elastic Debye temperature of 596 ± 7 K at 1.5 K. The acoustic mode heat capacity calculated from the latter is significantly smaller than the heat capacity measured by Wenger and Keesom at low temperatures. Following Wenger and Keesom, the difference is attributed to phasons (excitations involving the phase modulation of charge density waves). An average velocity is deduced for the phasons. 相似文献